A Novel Soybean Dirigent Gene Contributes to Promotion of Lignan Biosynthesis and Enhances Resistance to .

Phytophthora root and stem rot caused by the oomycete pathogen is a destructive disease of soybean worldwide. Plant dirigent proteins (DIR) are proposed to have roles in biosynthesis of either lignan or lignin-like molecules, and are important for defense responses, secondary metabolism, and pathogen resistance. In the present work, a novel gene expressed sequence tag is identified as up-regulated in the highly resistant soybean cultivar 'Suinong 10' inoculated with . The full length cDNA is isolated using rapid amplification of cDNA ends, and designated (GenBank accession no. HQ_993047). The full length is 789 bp and contains a 567 bp open reading frame encoding a polypeptide of 188 amino acids. The sequence analysis indicated that GmDIR22 contains a conserved dirigent domain at amino acid residues 43-187. The quantitative real-time reverse transcription PCR demonstrated that soybean mRNA is expressed most highly in stems, followed by roots and leaves. The treatments with stresses demonstrated that is significantly induced by and gibberellic acid (GA), and also responds to salicylic acid, methyl jasmonic acid, and abscisic acid. The GmDIR22 is targeted to the cytomembrane when transiently expressed in Arabidopsis protoplasts. Moreover, The GmDIR22 recombinant protein purified from could effectively direct -coniferyl alcohol coupling into lignan (+)-pinoresinol. Accordingly, the overexpression of in transgenic soybean increased total lignan accumulation. Moreover, the lignan extracts from transgenic plants effectively inhibits hyphal growth. Furthermore, the transgenic overexpression of in the susceptible soybean cultivar 'Dongnong 50' enhances its resistance to . Collectively, these data suggested that the primary role of GmDIR22 is probably involved in the regulation of lignan biosynthesis, and which contributes to resistance to .